No, you can't.  You can only transmit tax returns electronically to the IRS if you have a valid EFIN.

If you don't have an EFIN on your own but your firm is part of a business-related group of another ERO, that ERO may sponsor you for a separate EFIN, which you may use to transmit returns using PTO.  Note that this ERO will then be responsible for your adherence to the e-filing rules.

The alternative is for your clients to file the returns you prepare on paper but you must include a F.8948 with each paper return you prepare for your client to paper-file.